Casting easily oxidizable metals



Patented July 19, 1932 UNITED STATES PATENT OFFICE ROBERT THOMAS WOOD, OI LAKEWOOD, OHIO, ASSIIGNOR, BY'IESNE ASSIGNMENTS, TO MAGNESIUM DEVELOPMENT CORPORATION, A CORPORATION OF DELAWARE CASTING EASILY OXIDIZABLE METALS No Drawing. i

the atmosphere has been a serious obstacle to their successful casting in sand molds. In accepted foundry practice for ordinary metals there is usuall added to the sand or other similar molding materials a tempering medium, in most cases water, which imparts to the sand the properties necessary to satisfactory molding. It was accordingly supposed that in order to successfully cast magnesium and similar metals in such molds, the mold must be dried by careful heating in order to prevent attack of moisture on the molten metal.

To overcome the well known difliculties, several methods have been suggested. For example, it has been proposed, in conjunction with the drying method, to incorporate in the moldin material a substance which, when the mold Imcomes heated, will roduce a vapor around the metal to rotect it from the atmosphere. Obviously t e vapor of such a protective substance must have little or no effect on the metal. It has also been proposed to use certain protective substances such as sulfur, urea, oxalates, or boric acid, which are reported to be usable in an undried sand mold, in the belief that the vapors given off by these substances, when heated, would adequately isolate the metal and protect the same from attack b moisture in the mold. Practice, however, as shown that of these substances sulfur alone exerts a protective action sufiicient to dpermit'the use of water as a tempering me um if good castings of commercial size are to be produced.

In spite of the numerous investigations which have been undertaken relative to the Application filed October 28, 1929. Serial No. 401,960.

casting of the easily oxidizable metals in sand molds, the commercial foundry is still faced with difliculties when casting these metals. The drying of the mold is a tedious, expensive process and the incorporation of a protective substance has not been found to produce in all instances the desired effect. As stated above, sulfur may be employed to eliminate the necessity of drying the mold; but in this case also, the castings produced do not represent the optimum in desirable characteristics. I

The chief object of the present invention is to provide an improved method of utilizing the protective idea with easily oxidizable metals, to enable sound castings to be obtained, in a commercial foundry, of a good color and free, or substantially so, from oxid films and blow holes. Further objects are to provide a method for the production of sounder and cleaner castings of large size than has heretofore been considered possible; to provide new protective substances and molding mixtures containing the same, by which these methods may be carried out; and to modify and adapt some of the previously known protective substances so as to produce a more efficient protective effect, particularly in molds containing moisture. 1

My invention is developed from and predicated upon an investigation extending over a considerable period of time. In the course of this investigation, in which new and also previously known protective substances were used in both dried and undried sand molds and easily oxidizable metals, notably mag nesium and its alloys, were cast therein under varied commercial foundry conditions, I observed that while in the presence of some protective substances excellent castings might be made, there was a tendency for the castings to become less satisfactory as their size was increased. Although this had been previously noted, no method has been heretofore developed for satisfactorily overcoming the difliculty.

I have devised a method by which this difficulty may be overcome and good castings of a very considerable size may be produced. I have, moreover, found that this method produees betterv results with smaller castings than had heretofore, within my knowledge, been "obtained. My new method, briefly stated, comprises incorporating potassium sulfid in, the sand or other molding materials to provide a protective vapor around the casting as the mold is heated by the molten metal. The invention also includes the use of one or more other substances, capable of producing a metal-protecting vapor at successively higher temperatures, preferably such as toproduce collectively a substantially continuous emission of protective vapors as the tempor, regardless of the temperature to which perature of the mold rises, thus making possible the presence, in the mold and around the casting, of an adequately protective vathe mold is brought by the hot metal.

Most of the methods heretofore devised for casting magnesium or similar metals in .sand or the like required that the protective substances be incorporated in, the sand and that the mold made from this mixture be thoroug'hly dried before use in order to eliminate whatever water was added; to or was present in the sand. Of the protective substances.

suggested for use in such dried molds, the polyhydric alcohols and specifically glycerin had been found'to be especially efficacious. It had been thought, however, that such polyhydrie alcohols were eflicient only when used in dried sand molds. I have found that the contrary is true and that .when combined with other protective substances, for example sulfur, ammonium bisulfate, ammonium fluorid, naphthalene. and especially boric acid, these alcohols may be used in a moist sand mold with good results. This leads to important advantages, for in the older methods of using the polyhydric alcohols the sand longer necessary to add more alcohol than Wlll produce the desired protective eifect on the metal. Although glycerin has beenmentioned as the desirable polyhydric alcohol for use as a protective substance, I have found that when used in aqueous solutions ethylene glycol and di-ethylene glycol are markedly superior to glycerin in that substantially the same efl'ect is produced by the use of a 25 per cent aqueous solution of either ethylene or diethylene glycol as can be produced by the use of a 50 r cent solution of glycerin.

In usmg aqueous solutions of one of the mam polyhydric alcohols, such as ycerin,

ethylene glycol, or di-ethylene glyctfi, it was noted that with boric acid also present, re- 7 hydric alcohol and the boric acid at the elevated temperatures to which the mold is brought by the molten metal. Beilsteins Handbook of Organic Chemistry lists a compound having the formula (C H O B) which, it is stated, may be obtained by heating glycerin and bone anhydrid together.

My experiments indicate that when glycerin and boric acid are resent in the sand the compound described y Beilstein, or one much like it, is formed as the mold becomes heated. Possibly the compound produced when ethylene glycol is used has the analogous formula (C l 0 B) Whatever the actual composition may be, I use the expression organic borate hereinafter to include the compound just referred to and similar compounds, as for example the one listed in Beilstein above and the one formed by reaction between boric acid and di-ethylene glycol. At anyrate, by adding to the molding sand 2. compound formed by the reaction between boricacid and ethylene or di-ethylene glycol, which is presumably an ethylene borate, or, more gen-' erally, an organic borate, I have achieved practically the same results as those obtained with a mixture of boric acid and a polyhydric alcohol. lhe useof an organic borate alone, or of boric acid and a polyhydric alcohol without other protective substance, gives a protective effect on magnesium or like metals which is superior to that obtained with any one substance heretofore known to me, and the castings produced are in quality second only to those obtained in molds containing a plurality of protective substances of variant vaporizing temperatures. a In using boric acid and a polyhydric alcohol (with consequent formation of an organic borate when the metal is poured), I have found that excellent commercial results can be obtained by incorporating in the molding sand.

1 to 3 per cent (by weight) of boric acid and then adding to the mixture enough of a 25 to 75 per cent (preferably about 40 per cent) aqueous solution of ethylene or di-ethylene glycol to give the desired molding qualities. In molds formed of such sand I have produced magnesium and magnesium alloy castings', of distinctly superior quality, both from the standpoint of soundness and strength and from the standpoint of color. Other quantities of boricacid and other amounts of the same or another polyhydric alcohol may be mixed withthe sand and very good results ohtained. I have also found that as a substitute for boric acid ammonium borate may be employed; or borax and a mineral acid, say hydrochloric or sulfuric, which will react with the borax to produce boric acid. These substitutes will give, in combination with the polyhydric alcohol, substantiallly the same results as are obtained with boric acid and the same alcohol.

in the further course of my investigations 1 have found other substances, namely potassium sulfid and ammonium bisulfate, which when incorporated in the sand and heated by the molten-metal, also exert a protective action sufficient to make possible the production of good castings of the readily oxidizable metals, and they have, moreover, a protective action even in undried molds. These substances, potassium sulfid and ammonium bisulfate, may be used singly; or either may be used with other protective substances in the same mold. Each of them, when present as the only added protective substance, say to the amount or" about 2 per cent of the total solids of the mixture, will make possible the production of castings of limited size in undried sand molds. As between them, ammonium bi-sulfate is in general preferred. Moreover, either or both of these two substances, the protective properties of which were heretofore unknown, may be used advantageously in practicing my described method of producing large sized castings by means of a plurality of protective agents.

Other substances, some of them already known, may also be used in the above mentioned method. Among these are sulfur, am-

monium fluorid, urea, magnesium oxalate,

magnesium iiuorid, ammonium chlorid, and naphthalene. Many of these substances used singly as the protective substance in dried sand molds do not exert a very eflicient protective effect, and only certain of them have heretofore been supposed capable of exerting a protective action in the presence of moisture. For instance it has been believed heretofore that naphthalene is a successful protective substance only when it is mixed with dried sand, and in one instance at least the use of this compound, in combination with a resin, has been suggested to overcome the difficulties incident to molding when no water is used as a binder. I have found, however, that naphthalene in amounts of 7 to 10 percent by weight of the total mixture, exerts a protective eilect in moist sand which is in some cases adequate, especially for magnesium. I have also discovered that similar hydrocarbons, such as anthracene,,ichrysene,

etc., produce similar results and-I consider them to be substantial equivalent-s ofnaphthalene. All of the above mentioned protective substances I have used in carr ing out my novel method above described. ome are better than others but all, when used with other substances in accordance with my method, produce an eflect superior to that glycerin 290, sulfur 440, ammonium bisulfate 490. Boric acid volatilizes in steam and inpolyhydric alcohols. Ammonium fluorid has no true boiling point but it begins to vaporize and dissociate at comparatively low temperatures. Of ethylene boratc it can be said that when the compound is produced by heating ethylene glycol and boric acid in water to simulate the conditions occurring in a sand mold distillates are obtained from about 120 C. to as high as 280 which upon analysis are found to contain boron and organic matter. This is probably one reason why ethylene glycol and boric acid are so efi ective when used together. In some cases I prefer to use an organic borate, for example the ethylene borate just mentioned, as at least one of the plurality of protective substances, and sulfur as another, since I have found that molding mixtures containing the substances named are capable of producing better and larger castings than could heretofore be obtained. However, the pres ence of both these particular substances is not necessary to produce large sized castings or to produce smaller sized castings of a quality not heretofore obtainable, and in fact in some cases a combination containing only protective substances which were well known before my present invention, produces results superior to any which were theretotore obtained. Among substances usable alone, organic borate, sulfur, naphthalene, and ammonium bisulfate are especially eiiective, and one or more of these substances are included in each of the mixtures outlined below, but the invention is by no means limited in that respect. Instead of preparing in advance the organic borate which is formed (I believe) by reaction of the boric acid and ethylene or (ii-ethylene glycol, for example, it is in general more advantageous to produce the same in situ, so to speak, by incorporating the necessary reagents in the molding mixture. I may also use to advantage ammonium phosphate, the use of which is more fully described in the copending application of Francis C. Frary and myself, Serial No. 401,962, filed concurrently herewith.

In the following examples and in the ap pended claims the term sand is intended to include not only that articular material but sumlar 1nact1ve materials wl11ch,1n commonly accepted moldmg practice, are used to form molds of the agglomerated or non-permanent type. These examples (in which the parts statedare by we1ght) represent a number of molding compositions which have been found especmlly advantageous 1n casting the easily oxidizable metals and particularly magneslum and 1ts alloys, aecordmg to the pre- 1 ccpts of my invention. The water or other tempermg medium is added in amount sufiiclent to give the desired molding conslstency.

Example 1 I Molding sand; Approximately 90 parts 2 Sulfur Approximately 6 parts- Nnphthalene Approximately 4 parts Water). Suilicient Example 2 Molding sand .Approximately 89 parts r Approximately 6 parts Naphthalene Approximately 4 Paris Boric acid Approximately 1 part Water Sufficient Example 3 Molding sand Approximately 88 parts Sulfur Approximately 6 parts Naphthalene Approximately A parts Ammonium bisulfate Approximately 2 parts 1 Water. Suliicient V Examples .9 5

Molding sand Approximately 93 to 97 parts Sulfur Approximately 6 to 2 parts Boric acid Approximately 1 -lpart Di-ethylene glycol, 40 per cent aqueous solution Suflicient Snflicient Example 6 Molding sand Approximately 95 parts Sulfur Approximately 2 parts Naphthalene; Approximately 3 arts Dl-ethylene glycol, percent aqueous solution Su cient 40 Example 7 Approximately 94 parts Approximately 2 parts Approximately 3 parts Approximately 1 part Dl-ethylene glycol, 40 per cent aqueous solution Suillcicnt 7 Example 8 Molding sand Approximately 98 parts Potassium sulfid Approximately 2 parts Di-ethylene glycol, 40 per cent aqueous solution. Sufiicient Example 9,

Molding sand Approximately 93 to 91 parts Organic borate- Approximately 3 to 5 parts Naphthalenei Approximately 4 4 parts Water Sufllcient Example 10 Molding sand- Approximately QSpurts Approximately 2 parts 0 per cent aqueous solution- Sufilcient Ethylene glycol,

Ammonium bisultate--- Approximately 2 parts Boric acid Approximately 1 part Ethylene glycol, 40 per cent aqueous soliition Suflicient H V W Example 13 Moldin sand i Approximately 98 parts Ammon um fluorid Approximately 2 parts Ethylene glycol, 40 per cent aqueous solution" Snfflcient Example 14 Naphthalene Approximately 4 parts Boric acid Approximately 1 part Ethylene glycol, 40 per cent aqueous solution- Suiiicient Example 15 Molding sand Approximately 98 parts Boric acid Approximately 2 parts Ethylene glycol, 25 per cent aqueous solution- Suflicient Example 16 Molding sand Approximately 93 parts Naphthalene Approximately 4 parts Ammonium bisulfate Approximately 2 parts Boric ncld Approximately 1 part Ethylene glycol, per cent-aqueous solution- Suflicient Example 17 Molding sand Approximately 97 parts Ammonium blsulfate Approximately 2 parts Boric acid Approximately 1 part Ethylene glycol, 25 per cent aqueous solution- Suflicieut Example 18 Molding sand Approximately 90 to 88 parts Organic borate Approximately 3 to 5 parts Sulfur Approximately 2 2 parts Naphthalene Approximately 3 3 parts Ammonium bisulfute Approximately 2 2 parts Water Sufiicient Example 19 Molding sand Approximately 98 to 97 parts Borax odium tctraborate)- Approximately 2 to 3 parts Aqueous ution containing 15 er cent sulfuric acid :indO per cent ethy ene glycol-" Suficient Serial Nos. 401,957, 401,958, 401,950, 401,901,

and the aforesaid joint application of F rancis C. Fra-ry and myself, Serial No. 401,962, all filed of even date herewith. I

I claim- I 1.- The method of casting magnesium and other easily oxidizable metals in sand molds, comprising mixing with sand a plurality of protective substances of variant vaporizing temperatures, including potassium sulfid, boric acid and an aqueous solution of a polyhydric alcohol; forming a mold of the mixture; and casting the metal in the mold.

2. The method of casting easily oxidizable metals in sand molds, comprisingmixingwith sand a plurality of protective substances of variant vaporizing temperatures, including potassium sulfid, and boric acid and an aqueous solution of di-ethylene glycol; forming I a mold of the mixture; and casting the metal in the mold.

3. The method of casting easily oxidizable metals in sand molds, comprising mixing of variant vaporizing temperatures, includingpotassium sulfid, sulfur, naphthalene, and

bone acid and a solution of di-ethylene glycol; making a mold of the mixture; and castwith sand a plurality of protective substances and sand; forming a mold of the mixture; and casting the metal in the mold.

5. The method of casting magnesium and other easily oxidizable metals in sand molds, comprising mixing with sand potassium sulfid, sulfur, horic acid and a solution of a polyhydric alcohol; making a mold of the mixture; and casting the metal in the mold.

- 6. The method of casting magnesium and other easily oxidizable metals in sand molds, comprising casting the metal in a mold made of sand containing. in admixture therewith potassium sulfid and sulfur, and material adapted to produce a vapor of: an organic borate, and producing thereby around the metal in the mold a plurality of protective vapors including a vapor of an organic borate.

7. The method of casting magnesium and other easily oxidizable metals in sand molds,

comprising casting the metal in a mold formed of sand containing potassium sulfid,'

a'ndmaterial adapted to produce a vapor of an organic borate, and thereby producing around the metal in the mold a plurality of protective vapors including a vapor of an organic borate.

8. The method of casting magnesium and other easily oxidizable metals in sand molds,

.comprising mixing sand and a plurality of protective substances of variant vaporizing temperatures, including potassium sulfid,

forming a mold of the mixture, and casting the metal in the mold.

9. The method of casting easily oxidizable metals in sand molds, comprising mixing with the sand about 2 per cent of potassium sulfid, forming a mold of the mixture, and casting the metal in the mold.

10. The method of casting magnesium and other easily oxidizable metals in sand molds, comprising mixing potassium sulfid with the sand, forming a mold of the mixture, and casting the metal in the mold.

11. The method of casting magnesium and other easily oxidizable metals in sand molds, comprising mixing. sand and a plurality of protective substances of variant vaporizing temperatures, including potassium sulfide and a polyhydric alcohol, forming a mold of the mixture and casting the metal in the mold.

In testimony whereof I hereto aflix my signature.

ROBERT THOMAS ,WOOD. 

